Duplex translating-circtjits



J. R. CARSON.

v DUPLEX TRANSLATING CIRCUITS. APPLICATION FILED sins, 191s. RENEWED MAY 21,1919.

Patented June 15, 1920.

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DUPLEX TRANSLATING CIRCUITS. APPLICATION FILED SEPT.5, IQHS BENEWED MAY 27,1919.

1,343, 306. Patented June 15, 1920'.

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IIVVENTOI? John R. Carson ATTORNEY 1. R. mason. DUPLEX TRANSLATING CIRCUITS. APPLICATION FiLED SEPTA), I916- RENEWED HAY 27,1919- 1,343,306. Patented June 15, 1920.

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DUPLEX TRANSLATING CIRCUITS.

APPLICATION FILED SEPT.5. I916. RENEWED MAY 27, 1919.

1,343,306. Patented June 15, 1920.

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JOHN R. CARSON, 0F IVIONTCLAIR, NETV JERSEY, ASSIGNOR TO AMERICAN TELEPHONE AND TELEGRAPH COJNIPANY, A CGRPGRATION OF NEW YQRK.

Application filed September 5, 1916, Serial No. 118,573.

To all whom it may concern:

Be it known that 1, JOHN E. Carson, residing at Montclair, in the county of Essex and State of New Jersey, have invented certain Improvements in Duplex Translatinglircuits, of which the following is a specification.

This invention relates to signaling circuits and has for its general object the provision of a duplex translating system which is capable of a wide range of utility and which shall exhibit a high degree of ciency in the various applications of which it is capable.

In its general embodiment the invention comprises a duplex translating structure having a pair of input and a pair of output circuits, the pair of input circuits being symmetrically associated with one source of current variation, and oppositely associated with a second source, the output circuits being differential with respect to one outgoing or receiving circuit and cumulative with respect to another outgoing circuit. Thus the first mentioned source produces by virtue of its symmetrical connections potential fluctuations the same phase in the two input circuits, while the second mentioned source, by virtue of the fact that the input circuits are oppositely associated therewith, produces potential fluctuations of opposing phase in said input circuits. This statement is made to define the significance attached to sym metrical and opposite connections in this specification.

Thus in general there may be four main elements comprising two sources and two receiving circuits which may be variously related to the translating device proper. :rdditional results may be produced by the omission of one or more of the four main elements, with corresponding changes in the connections of the remaining elements. The form of translating device used may preferably be of the thermionic vacuum tube type, though this invention is not limited to any particular type of translating device. It will be understood that the term translating device embraces broadly an apparatus or relay capable of amplification, detection or modulation of signal waves.

Tn its more specific aspects the invention has for one of its objects the provision of translating circuit with a feed back connection between output and input circuits for Specification of Letters Patent.

Patented June 15, 1920.

Renewed May 2'7, 1919. Serial No. 300,178.

the reamplification of signal waves, in which the tendency to sing which is inherent in such arrangements is substantially eliminated.

A further object has reference to the modulation of high frequency or carrier currents by low frequency signaling currents, by means of an arrangement in which the carrier currents shall-be suppressed except at such times as low frequency si nalmg currents are applied to the circuit. buch a structure is capable also of functioning, in combination with a local source of high frequency energy, as an improved detector in which distortion is largely eliminated.

A still further object of the invention is the provision of a selective receiving apparatus for multiplex carrier wave signaling, in which the necessity for high frequency tuning and selectivity is eliminated.

The invention will be more fully understood by reference to the drawing in which Figures 1, 2, 3 and 3 represent four modifications of the improved non-singing feed back circuit. Fig. at is a diagram of a modulating system for high frequency carrier wave signaling in which the carrier current used for transmission is suppressed except when modulated at low frequency. The modulating device employed is of the thermionic type. Fig. 5 is a diagram of a similar circuit using a mechanical repeater, while Figs. 6, 7 and 8 illustrate three modifications of a selective receiving system for multiplex carrier currents. l3 9, l0 and 11 are curves illustrating the action of the apparatus.

Referring now to Fig. l, in which all of the essential elements of this invention are disclosed, a pair of three element thermionic tubes having filaments l, 2, grids 3, 4i and plates 5, 6 are provided, the filaments being heated by a battery 7. The tubes are preferably similar and equal in their structure and characteristics. They are then equivalent to and may be replaced by a single duplex tube as shown in the succeeding figure. The input circuits of the tubes are arranged in parallel with respect to the secondary 8 of a transformer 9 in the common conductor of the two input circuits, the primary 10 of the transformer being included in a circuit 11 leading to a source of potential variations. Condensers 12, 1.8 are inserted. in the input circuits, and the secondary 1st of a trans forn'ier 15 is shunted about the two con densers.

The output circuits are also connected in parallel with respect to a battery 17 and the primary 18 of a transformer 19 in the common conductor. The secondary 20 of the transformer is connected by a feed back circuit 21 to the primary 16 of transformer 15. Each output circuit contains a primary winding of a three Winding transformer 22, the coil in circuit with the plate 5 being designated 23, and that corresponding to plate 6 being designated at, coils 23 and24l being wound in the same direction. The secondary 25 is connected to an outgoing circuit 26 leading to a receiving or other translating device.

An analysis of this organization shows that there are two sources of potential variation, one symmetrically applied to the input circuits through transformer 9 and consequently producing potential variations of substantially the same phase, and the other oppositely applied tothe two input circuits through transformer 15 so as to produce potential variations of opposing phase. There are also two outgoing circuits, one being or mulatively or symmetrically connected to the output circuits of the translating device through transformer 19, and the other beingdifierentially or oppositely coupled through the transformer 22. These four elements are characteristic of the invention in its fundamental form, and may be variously interconnected to produce different results, and in some instances certain of the elements may be omitted as will be clear from an inspection of certainof the modifications hereinafter described.

A slight modification of the organization of Fig. 1 is illustrated in Fig. 2, the same reference characters being applied to identical parts in the two diagrams. The essential. difference is that while in Fig. 1 coils 23 and 24 are wound in the same direction, in Fig. 2 they are wound in opposite directions, this change producing a marked effect on the operation of the apparatus as will hereinafter appear. A further difference resides in the tuning adjustments of circuit 26. It will also be noted that while in Fig. 1 two thermionic tubes are used, each having a filament, grid and plate, in Fig. 2 the two tubes are combined in a single tube, with a common filament 27, but separate grids and plates. These two structures are equivalent and it is to be understood that either arrangement may be used in any of the organizations herein illustrated which make use of the thermionic form of repeater.

The action in Fig. 1 is as follows: High frequency oscillations being impressed upon circuit 11 act through the transformer 9 to impress potential variations of substantially the same magnitude and phase on the grids 3 and 1, so that amplified fluctuations of current of substantially the same phase flow in the output circuits leading to the plates 5 and 6. These fluctuations produce no effeet in the transformer 22 owing to the fact that primaries 23 and 2a are wound in the same direction and hence the action of the amplified fluctuations is differential with respect to secondary 25. The coupling of coil 25 to coils 22-3 and 2a n'iay be adjusted for exact neutralization. However they act cumulatively thronglrthe transformer 13) to induce amplified oscillations in the feed back circuit 21. These oscillations now act through the transfm'mer 15 to apply equal potential variations of substantially opposing phase to the grids 3 and t, thus producin amplified fluctuations of opposing phase in the output circuits. These fluctuations neutralize in the primary 18, but have cumulative effects in primaries 23 and iland hence amplified oscillations will be set up in the outgoing circuit 26 which is preferably tuned to the high frequency oscillations.

The action in the modified circuit of Fig. 2 somewhat different. In this case, assuming high frequency oscillations modulated by low frequency signals to be impressed on circuit 11, equal fluctuations of potential of the same phase are applied to grids 3 and at thereby causing amplified fluctuations of substantially the same phase in the steady current due to battery 17 in the two output circuits. These fluctuations act cumulatively through transformer 19 to produce amplified oscillations in the feed back circuit 21. Due to the fact that the winding of primary 2a is opposite to that of primary 23, the fluctuations in the two output circuits are added to each other and tend to induce through induction coil 22 amplified oscillations in output circuit 26. However, owing to the fact that this circuit is tuned to the low frequency signaling currents or at any rate is so tuned us to cut out the high frequency, no appreciable result occurs in the output circuit. The amplified oscillations in feed back circuit 21 act through transformer 15 to apply equal variations of potential of opposing phase to grids 3 and 4. The detecting property of the tube now comes into play, and owing to the opposite winding of coils 2 and 2+ the high frequency re-amplified fluctum tions in the output circuits are neutralized. but the detected low frequency variations act cumulatively through transformer 22 to produce low frequency variations in the circuit 26. It will be noted that in both Figs. 1 and 2 the feed back coupling is differential or opposite with respect to the input and cumulative with respect to the output circuit, so that the tendency to sing through this circuit is substantially eliminated.

It will be recalled that while in Fig. 1

there is a double amplification of the input currents, in Fig. 2 the high frequency currents are first amplified and then detected. Thus while the arrangement of Fig. 1 is adapted to reamplify currents of either high or low frequency, that of Fig. 2 is adapted for use primarily only with high frequency carrier wave systems. In order to better understand the reason for this difference in action attention is called to the curves of Figs. 9, 10 and 11. Fig. 9 is a characteristic curve of one of the vacuum tubes employed in this invention, the curve being a plot of the relation between the grid-filament voltage and the wing or output current. Assuming that at zero potential on the grid a steady wing current of value O is flowing, if alternating potential varying from minus V to plus V be applied between grid and filament, the wing current will fluctuate between values O and C. Owing to the bend in the curve the increase in current flow exceeds the decrease (at this particular point on the characteristic curve) and if these fluctuations occur at high frequency there will be an average increase of current flow in the wing circuit this phenomenon representing the detecting power of the device. On the other hand, due to the slope of the curve the current fluctuations in the output circuit may be much greater than those in the input circuit. This is the so-called amplifying ef fect. From this it will be seen that the same tube may function both as an amplifier and a detector.

Considering now the curves of Figs. 10 and 11, Figs. 10. and 11 represent exaggerated graphs of the current in the output circuits of plates 5 and 6 respectively, due to equal steady alternating grid potential variations of opposing phase neglecting the distortion in form which always occurs in a vacuum tube. A comparison of these curves shows that the fluctuations in the two wing circuits are opposite when the grid potential variations are opposing, while the average increase in current flow, represented by the difference between C and O, in both diagrams, is in both cases an increase in the same direction. Now in order to get a cumulative effect of the indi vidual waves or an amplification, when the grid potential variations are opposing or of opposing phase, it is evident that the outgoing circuit must be differentially related to the two output circuits proper, while if the grid potential variations are of the same phase, the outgoing circuit must be cumu iatively related. On the other hand to get a cumulative effect of the difference between. the two halves of a wave, which corresponds to the average current increase to C, the outgoing circuit must be always cumulatively or symmetrically related to the two output circuits proper irrespective of whether the grid potential variations are of the same or opposing phase, since otherwise the resultants would neutralize each other. As in amplification it is the indi vidual waves which are received and trans mitted to the outgoing circuit while in detection it is the low frequency variations in the resultant C which are received and transmitted, it becomes apparent that the reversal of winding 24: with respect to 23 in Fig. 2 results in detected variations pass ing into circuit 26, the individual amplified high frequency waves neutralizing each other, while in Fig. 1, the amplified high frequency waves pass, while the detected low frequency variations neutralize each other.

Fig. 3 shows still another feed back arrangement. In this case the incoming circuit terminates in a primary 2'? of a transformer 28, the secondary 29 of which is con nected across the two input circuits. The output circuits include primaries 30 and 31 of a transformer 32, the secondary 33 of which connects through feed back 21 to the primary 34 of transformer 35, the secondary 36 of said transformer being included in the common branch of the input circuits. A. primary 37 of induction coil. 38 is located in the common branch of the output, the secondary 39 being connected with the outgoing circuit 26.

This arrangement also produces a double amplification. High frequency oscillations coming in over circuit 11 impress potential variations of substantially opposing phase upon grids 3 and l, thereby producing amplified current fluctuations of opposing phase in the two output circuits. Coils 36 and 31 being wound in the same direction, the fluctuations act cumulatively through transformer 32 to impress amplified oscillations on feed back circuit 21 which, acting through transformer 35 causes potential. variations of substantially the same phase upon grids 8 and 4;, thereby producing reamplified fluctuations of substantially the same phase in the output circuits. These fluctuations being in phase with each other are neutralized in transformer but act cumulatively through transformer 38 to produce amplified oscillations in outgoing circuit 26. By reversing either winding 36 or 31 as shown in Fig. 3, the low frequency variations in amplitude of the oscillations imposed on the tube from circuit 1.1 will be detected and the detected currents will. impress corresponding low frequency variations upon circuit 21, the amplified high frequency fluctuations being neutralized by windings 80 and 81. The detected currents in feed back 21 passing through transformer will be amplified and impressed upon cir' cuit 26. As in the case of Fig. 2, a filter or other arrangement is provided in the outgo ing circuit 26 to prevent the high frequency oscillations from being transmitted through the transformer 38 to the line.

In Fig. IV a scheme for modulating high frequency carrier currents by means of low frequency signaling currents is illustrated, the carrier currents being suppressed when the modulating currents are not applied. In this figure a source of high frequency oscillations L0 is connected to the common conductor of-the input circuits through a transformer 41. An incoming circuit d2, leading to a source of low frequency signaling current such, for example, as a telephone transmitter is connected to the primary 43 of a transformer 44, the secondary d5 of which is bridged across the two input circuits in parallel with condensers l2 and 13. The output circuits are provided with primaries 46 and 47 of a transformer 48, the secondary 49 of which is connected to an outgoing circuit 50. Normally, when no currents are impressed upon circuit 42-, the high frequency oscillations from source 40 acting through transformer 41 impress equal voltage variations of the same phase upon grids 3 and 4:, thereby producing equal fluctuations of the same phase in the output circuits. Coils 4L6 and d7 being wound in the same direction, circuit 50 is differentially coupled to the two output circuits the fluctuations neutralize each other and no effect is produced on circuit 50. When however, low frequency current variations from circuit 41-2 are impressed upon the repeater circuit through transformer 44:, the high frequency potential variations are augmented upon the one grid and decreased upon the other, pro ducing correspondingly augmented fluctuations in the one output circuit and correspondingly reduced fluctuations in the other. The fluctuations in the output circuits are no longer balanced and consequently oscillations are produced in the outgoing circuit 50 which have an amplitude proportional-to the instantaneous value of the low frequency modulating currents coming from circuit 4-2. It is therefore seen that the carrier waves are suppressed except when signaling currents are applied.

Fig. 5 is an equivalent arrangement using a mechanical repeater instead of thermionic vacuum tubes. In this arrangement two parallel oscillation circuits having 'ariable resistances 51 and 52, and condensers and 54 therein are provided with acommon conductor in which is inserted the secondary of a transformer 56, the primary 57 of which is in circuit with a source of high frequency oscillations 40. Primary windings 46 and 47 of a transformer 4-8 are also included in the circuits, while the secondary 4:9 is connected to outgoing circuit 50. A mechanical repeater comprising a receiver coil. 58 and a differential or push and pull microphone is provided, the receiver coil 58 being in a circuit 42 leading to a source of low frequency modulating or naling currents, and the electrodes 59 and U0 of the microphone being connected in the two oscillation circuits, with the common electrode (51 connected to the common conductor thereof. High frequency oscillations from source el-O are normally neutralized in windings l6 and 4-7. \Vhen however modulating currents flow in circuit 42, the receiver a ts to correspondingly vibrate the electrode 6]., so that the resistance in one circuit is increased and in the other is decrcased, with the result that the osuillations in the one circuit are increased while those in the other circuit are simultnncmisly decreased. The oscillations are therefore no longer balanced in windings it) and at? and consequently oscillations are impressed upon circuit 50 through transformer 48, having an amplitude proportional to the incoming low frequency currents of circuit 42. It will be seen from this that the mechanical rep rater is equivalent to the thermionic tube modulator of Fig. l, and it will be under stood that the arrangement is not restricted to any particular type of translating or modulating device. Furthermore the arrangement of Fig. lis not limited to function only as a modulating system in carrier wave signaling, but may be employed as a duplex distortionless detector as illustrated in Figs. 6, '7 and S.

In Fig. 6 a receiving apparatus for multiplex carrier wave telephony is illustrated. By this arrangement it is possible to filter out the desired signal at low frequency instead of filtering at high frequency as has been necessary heretofore. In this arrangement the plurality of carrier currents are led in over a circuit 62 which terminates in the primary (33 of a transformer (54;, having two secondary windings 65 and (50, one included in each of the input circuits of the repeater. A loca source of high frequency is supplied by a homodyne or heterodvne generator 67 which coupled through a transformer 68 to the common conductor of the two input circuits. It will be understood that a heterr'idynegenerator a source of alternating current energy of frequency differing from that of the incoming carrier wave by a preassigned frequency preferably within the limits of audition. while a homodyne generator is a source of energy of frequency identical with that of the incoming arrier wave. The former is employed when unmodulated carrier waves are transmitted, while the latter is preferably employed when the carrier wave is modulated as in carrier wave telephony. In each output circuit is inserted a primary winding of a transformer (39, the winding in circuit with plate 5 being designated and that in circuit with plate 6 being designated 71. The secondary '72 of the transformer is connected to a circuit '73 leading through a low frequency filter (not shown) to a receiving instrument. The filter to be used is of a well known type of broad band filter which will suppress all frequencies above a certain limit, but permit the passage without attenuation of all frequencies below this limit, which. for telephonic purposes might be fixed at 2500 cycles. This type of filter is disclosed and. fully described in U. S. patent of G. A. Campbell, No. 1,227,113, issued May 22, 1917.

The operation of the apparatus will be understood from the following considerations:

It has been pointed out in a U. S. patent issued to Maurice Le Blane, No. 857079 of June 18, 1907, that when a plurality of carrier currents of different frequencies, each modulated by voice currents are sent out on a line, and at a receiving station a frequency equal to that of one of the carriers is provided, this frequency will interact with the modulated carrier current having the same period, with the result that a suitable receiving instrument will respond to the low frequency voice currents by which that particular carrier is modulated, while carriers having a different frequency will be without effect. A full theoretical discussion of the principles involved are given in the above patent and need not here be repeated, it be ing suflicient to point out that if a plurality of carrier waves having frequencies f,, 7", f be sent out on the line, each modulated at audio frequency 10, and further if at the receiving station a homodyne frequency f equal to the frequency of one of the carrier waves be allowed to interact therewith, a plurality of frequencies will result in the output circuits of the repeater structure of Fig. 6 as follows:

Assuming that the homodyne frequency 71. is equal to frequency f the last four frequencies reduce to 2f +p) (W -p) p and -79. If the carrier frequencies differ from each other by an amount greater than 2p it will be clear that all of the frequencies above set forth except 7? and p will be greater than 19. Hence a filter in the outgoing circuit which suppresses all frequencies above p will suppress everything except the audio frequency by which carrier frequency f was modulated. The signals by which other carriers were modulated will not be received because the resultant frequencies due to their interaction with the carrier frequency and the homodyne frequency will be greater than go. It will now be apparent that by applying the homodyne frequency to the common conductor of the input circuits of Fig. 6 through transformer 68, so that this frequency interacts with the several incoming carrier frequencies modulated by low frequency signals, the various resultant frequencies above set forth will appear in the output circuits of the repeater and be impressed on outgoing circuit 73 through transformer 69, the filter acting to suppress everything except the voice currents which modulated the carrier current having the same frequency as the homodyne generator. The same effect will be produced if the incoming carrier currents are impressed upon the translating circuits through transformer 68, and the homodyne frequency be impressed through transformer 64:. An additional advantage to be obtained by this arrangement is that, owing to the neutral connection of the homodyne generator with respect to the incoming line, the energy from the generator does not react upon the line and cause a tone in other receiving devices upon the same line. A further advantage attaching to the use of duplex translating arrangements resides in the fact that distortion of the incoming signal which is always and inherently caused by ordinary detectors is substantially eliminated by the combination of the duplex detector with a local homodyne generator. Consequently the utility of the duplex detector is not lim ited to its use in combination with a filter nor is it limited to use in a multiplex system.

A slight modification is shown in Fig. '7 in which the incoming carrier currents are impressed upon the input circuits of the duplex detector by a conductive connection instead of by an inductive connection such as shown in Fig. 6. The two sides of the incoming line 7 1 are directly connected to the grids 3 and 4, and are bridged by substantially equal resistances 75 and 76 to the mid-point of which the common conductor of the input circuits of the detector is connected, the homodyne currents being applied just as in Fig. 6. The operation is similar to that already described in connection with Fig. 6.

In Fig. 8 an alternative arrangement is shown in which the incoming line 77 is directly connected in the common conductor of the two input circuits of the repeater, while the homodyne currents from generator 67 are applied through a transformer 78, having secondary windings 80 and 81, one in each of the input circuits. The operation of this circuit is similar to that of Figs. 6 and 7. It will be understood that the arrangements of Figs. 6, 7 and 8 are essentially equivalent and that the particular connections are immaterial provided that of the two sources of potential variations one is applied symmetrically or cumulatively and the other oppositely to the two input circuits toproduce widely varying results.

and that the receiving circuit 73 is differentially coupled to the two output circuits. It will be further understood that while two similar tubesare shown a single duplex tube, 'suchfas that: shown in Fig. 2 may beequally "well or even preferably employed.

It will be seen that by this invention a duplex translating system'has been devised which is bothsimple'and eflicient and which is capable of'a large'nuinber of applications lVhile the invention has been illustrated as enibodie'd in alimited number of forms it will beun'derstood that the embodiment may be widely varied without departing from the scope of the appended claims.

What is claimed is:

1. A'itranslating apparatus comprising a duplex translating arrangement, apair of input and a pair of output circuits for said translating arrangement, two separate sources of current variation, and two separate outgoing circuits, said input circuits being symmetrically*associated with one of 'saidsources and'bein'g oppositely associated with theothersource, said output circuits being cumulatively associated with one of said outgoing circuitsand being differentially associated with the other outgoing circuit.

2. A translating apparatus comprising a pair of translating devices, two separate sources of :current variation and two separate outgoing circuits, said translating devices being symmetrically associated with one of said sources and being oppositely as sociated' with the other source, saidtranslating "ClBVICGS being alsofcumulatively associated with one of said outgoing circuits and 40 of current variations, said repeater circuits being s'ynnnetrically associated with one of 'said sources and being oppositely associated Wjith'theothersourca' and an outgoing circuit as'soc ated With said repeater circuits.

A translating apparatus comprising a pair of repeatercircuitaa source of current variation associated with'said repeater circuits, and a pair of outgoing-circuits, said repeater "circuits bei'ng cumulatively 'associated with one of said outgoing circuits and being differentially associated with the other.

7. In a translating apparatus, a duplex translating arrangement comprising a pair of grids and a pair of plates, a pair of input circuits, one connected to each grid and hav ing a common conductor, a pair of output circuits, one connected to each plate and having a common conductor, and two separate sources of current variation, said input circuits being in pa 'allel with respect to one of said sources and in series with respect to the other of said sources.

8. In a translating apparatus, a duplex translating arrangement comprising a pair of grids and a pair of plates, a pair of in' put circuits, one connected to each grid and having a common conductor, a pair of output circuits, one connected to each plate and having a common conductor, and two separate outgoing circuits,-one of? said outgoing circuits being associated with the common conductor of the output circuits, and the other outgoing circuit being serially associated with the twoplatcs.

9. A translating apparatus comprising a duplex translating arrangement, a pair of input and a pair of output circuits for said translating arrangement, each pair of circuits having a common conductor. a source of current variations associated with said input circuits, an outgoing circuit associated with said output circuits, and a feed back circuit associated with the common conductor of one of said pairs of circuits, and serially associated with the other pair of circ'uits.

10. A translating apparatus comprising a duplex tanslating arrangement. a pair of input and a pair of output circuits for said translating arrangement, each pair of circuits having a common conductor and a source of current variations associated with the common ('0]l(l'll('1i1(ll of the input circuits. an outgoing circuit associated with both of said output circuits and a "feed back circuil associated with the common conductor ol the output circuits and serially associated with the two input circuits.

11. A translating apparatus comprising a pair of repeater circuits, two separate sources of current variations, and two outgoing cir cuits, said repeater circuits being symmetrically associated with one of said sources and being oppositely associated with the other source, and said outgoing circuits being as sociated with said repeater circuits.

12. Atranslating apparatus comprising a duplex translating arrangement, a pair of input and a pair of output circuits for said translating arrangement, two separate sources of current variation, and two separate outgoing circuits, said input circuits being symmetrically associated with one ol saidsources and being oppositely associated with the other source, and said outgoing cir cuits being associated with said output circuits.

13. A translating apparatus comprising a duplex translating arrangement, a pair of input and a pair of output circuits for said translating arrangement, two separate sources of current variations, and an outgoing circuit, said input circuits being symmetrically associated with one of said sources and being oppositely associated with the other source, and said outgoing circuit being associated with both of said output circuits.

14. A translating apparatus comprising a duplex translating arrangement, a pair oi input and a pair of output circuits for said translating arrangement, a source of current variations associated with said input circuits, an outgoing circuit associated. with. said output circuits, and a feed back connection connecting saidoutput and input circuits, the association of said input circuits with respect to said source and said feed back connections being symmetrical as to the one and opposite as to the other.

15. A translating apparatus comprising a duplex translating arrangement, a pair of input and a pair of output circuits for said translating arrangement, a source of current variations associated with said input circuits, an outgoing circuit associated with said output circuits, and a feed back connection connecting said output and input circuits, the association of said input circuits with respect to said source and said teed back connections being symmetrical. as to the one and opposite as to the other, and the association of the output circuits with said outgoing circuit and feed back connection being cumulative as to the one and (iiiferential as to the other.

16. A translating apparatus comprising a duplex translating arrangement, a pair oi input and a pair oi? output circuits for said translating arrangement, an independent circuit, an induction coil having a winding in the output circuits and a winding in. said independent circuit, an incoming circuit associated with said input circuits, and an outgoing circuit associated with said output circuits.

1'7. A translating apparatus comprising a duplex translating arrangement, a pair of input and a pair of output circuits, said out put circuits having a common conductor, and a plurality of independent circuits, one associated with both input circuits, one associated with said. common conductor and one associated with individual conductors of each of said output circuits.

18. A translating apparatus comprising a duplex translating arrangement, a pair of input and a pair of output circuits for said translating arrangement, said output cir cuits including a common path, two separate sources oi? current variation and two separate outgoing circuits, said sources being associated with. said input circuits and said outgoing circuits being associated with said output circuits, at least one of said outgoing circuits being associated with said common path.

19. A translating apparatus comprising a duplex translating arrangement, parallel circuits for said translating arrangement, including a common path and individual paths, a plurality oi independent circuits including two incoming circuits and an out going circuit, one of said independent circuits being associated with said common path and the others of said circuits being associated with said individual paths.

20. A translating apparatus comprising a duplex translating arrangement, parallel cir cuits for said translating arrangement in.- cluding a common path and individual paths, conductive evacuated gaps in said individual paths, two sources of potential variations associated with said circuits, one of said sources being associated with said common path.

21. A translating apparatus comprising a duplex translating arrangement, parallel circuits for said translating arrangement including a common path and individual paths, conductive evacuated gaps in said individual paths, two sources of potential variations associated with said circuits, one of said sources being associated with said common path and the other of said sources being associated with said individual paths.

22. A translating apparatus comprising a pair of parallel circuits including a common path and individual paths, translating devices in said individual. paths, two sources of potential variations associatedv with said circuits, one of said sources being of relatively high frequency, and the other of relatively low frequency, one of said sources being associated with said common path and the other of said sources being associated with said individual paths.

In testimony whereof, I have signed my name to this specification in the presence of a subscribing witness, this twenty-eighth day of August, 1916.

JOHN R. CARSON.

lVitness:

C. C. Ross. 

